betadex and thermozymocidin

Glucose is a preferred metabolite in most mammalian cells, and proper regulation of uptake is critical for organism homeostasis. The glucose transporter 1 (GLUT1) is responsible for glucose uptake in a wide variety of cells and appears to be regulated in a tissue specific manner. Therefore, a better understanding of GLUT1 regulation within its various cellular environments is essential for developing therapeutic strategies to treat disorders associated with glucose homeostasis. Previous findings suggest that plasma membrane subdomains called lipid rafts may play a role in regulation of GLUT1 uptake activity. While studying this phenomenon in L929 mouse fibroblast cells, we observed that GLUT1 associates with a low density lipid microdomain distinct from traditionally-defined lipid rafts. These structures are not altered by cholesterol removal with methyl-β-cyclodextrin and lack resistance to cold Triton X-100 extraction. Our data indicate that the GLUT1-containing membrane microdomains in L929 cells, as well as GLUT1's basal activity, are instead sphingolipid-dependent, being sensitive to both myriocin and sphingomyelinase treatment. These microdomains appear to be organized primarily by their lipid composition, as disruption of the actin cytoskeleton or microtubules does not alter the association of GLUT1 with them. Furthermore, the association of GLUT1 with these microdomains appears not to require palmitoylation or glycosylation, as pharmacologic inhibition of these processes had no impact on GLUT1 density in membrane fractions. Importantly, we find no evidence that GLUT1 is actively translocated into or out of low density membrane fractions in response to acute activation in L929 cell.

Topics: Animals; beta-Cyclodextrins; Biological Transport; Cell Line; Fatty Acids, Monounsaturated; Fibroblasts; Glucose; Glucose Transporter Type 1; Membrane Lipids; Membrane Microdomains; Mice; Octoxynol; Sphingomyelin Phosphodiesterase

Clostridium difficile toxin (CDT) is a binary actin-ADP-ribosylating toxin that causes depolymerization of the actin cytoskeleton and formation of microtubule-based membrane protrusions, which are suggested to be involved in enhanced bacterial adhesion and colonization of hypervirulent C. difficile strains. Here, we studied the involvement of membrane lipid components of human colon adenocarcinoma (Caco-2) cells in formation of membrane protrusions. Depletion of cholesterol by methyl-β-cyclodextrin inhibited protrusion formation in a concentration-dependent manner but had no major effect on the toxin-catalyzed modification of actin in target cells. Repletion of cholesterol reconstituted formation of protrusions and increased velocity and total amount of protrusion formation. Methyl-β-cyclodextrin had no effect on the CDT-induced changes in the dynamics of microtubules. Formation of membrane protrusions was also inhibited by the cholesterol-binding polyene antibiotic nystatin. Degradation or inhibition of synthesis of sphingolipids by sphingomyelinase and myriocin, respectively, blocked CDT-induced protrusion formation. Benzyl alcohol, which increases membrane fluidity, prevented protrusion formation. CDT-induced membrane protrusions were stained by flotillin-2 and by the fluorescent-labeled lipid raft marker cholera toxin subunit B, which selectively interacts with GM1 ganglioside mainly located in lipid microdomains. The data suggest that formation and especially the initiation of CDT-induced microtubule-based membrane protrusions depend on cholesterol- and sphingolipid-rich lipid microdomains.

Topics: Anti-Bacterial Agents; Antifungal Agents; Bacterial Adhesion; Bacterial Toxins; beta-Cyclodextrins; Caco-2 Cells; Cholesterol; Clostridioides difficile; Dose-Response Relationship, Drug; Enterocolitis, Pseudomembranous; Fatty Acids, Monounsaturated; Humans; Membrane Microdomains; Microtubules; Nystatin; Sphingolipids; Sphingomyelin Phosphodiesterase

Lipid rafts are involved in the life cycle of many viruses. In this study, we investigated the role of lipids in the life cycle of vesicular stomatitis virus (VSV). Cholesterol depletion by pretreatment of BHK cells or VSV particles with methyl-beta-cyclodextrin (MbetaCD), a cholesterol-sequestering drug, inhibited the production of VSV dramatically. This effect was reversible, and virus production was restored by the addition of cholesterol, indicating that the reduction was caused by the loss of cholesterol in the cell membrane and virus, respectively. Cholesterol depletion at the adsorption stage also reduced the production of VSV significantly, but in contrast, only had a limited effect on virus production at the post-entry stage. Inhibition of sphingomyelin by myriocin treatment only showed a minor effect on VSV production. However, reduction of cholesterol and sphingomyelin at the same time dramatically reduced VSV production, showed a significant synergistic effect. These results suggest that lipid rafts play an important role in the life cycle of VSV.

Topics: Animals; beta-Cyclodextrins; Cell Line; Cell Survival; Cholesterol; Cricetinae; Fatty Acids, Monounsaturated; Membrane Microdomains; Sphingomyelins; Vesiculovirus; Virus Internalization

Rod and cone photoreceptor cyclic nucleotide-gated (CNG) channels play pivotal roles in phototransduction. This work investigates the functional significance of photoreceptor CNG channel association with membrane microdomains enriched in raft lipids, cholesterol and sphingolipids. The primary subunits of cone and rod CNG channels, CNGA3 and CNGA1, respectively, were heterologously expressed in HEK 293 cells, and channel activity was determined by ratiometric measurement of [Ca (2+)] i in response to cyclic guanosine monophosphate (cGMP) stimulation. CNGA3 was found to be largely insoluble following Triton X-100 extraction and cofractionationed with biochemically isolated membrane domains enriched in caveolin-1. Cofractionation of both natively expressed CNGA3 and CNGB1 (the modulatory subunit of the rod CNG channel) with the low buoyant density, caveolin-1-enriched membranes was also confirmed in mouse retinas. The functional significance of this association was established by the observed negative effects of depletion of raft lipids on the channel activity. Treatment with the cholesterol depleting agent, methyl-beta-cyclodextrin (MCD), significantly inhibited CNGA3 and CNGA1 activation in response to cGMP stimulation. MCD treatment lowered cellular cholesterol levels by approximately 45% without altering fatty acid composition, suggesting that the inhibition of channel activity by MCD treatment is not due to perturbation of other membrane lipids. Treatment with the sphingolipid biosynthesis inhibitor myriocin resulted in impaired activation and cytosolic redistribution of CNGA3, suggesting that the integrity of the membrane domains is critical for the channel cellular processing and plasma membrane localization. This study demonstrates the association of photoreceptor CNG channels with membrane domains enriched in raft lipids and indicates, for the first time, that raft lipids modulate the plasma membrane localization and functional activity of photoreceptor CNG channels.

Topics: Animals; beta-Cyclodextrins; Cell Membrane; Cells, Cultured; Cholesterol; Cyclic Nucleotide-Gated Cation Channels; Fatty Acids, Monounsaturated; Humans; Kidney; Membrane Lipids; Membrane Microdomains; Retina; Sphingolipids